# Base Mainnet ETH Balance Lookup

> Base Mainnet ETH Balance Lookup is a paid API for AI agents from x402-data-api.sigrunner.workers.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-16).

Returns the ETH balance (in ETH and USD) for a given Base mainnet wallet address.

## Facts

- Endpoint: GET https://x402-data-api.sigrunner.workers.dev/chain/balance
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-mainnet-eth-balance-lookup-17bb65be
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_QW32QWTpXcaLRAA8E10QH

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability base-mainnet-eth-balance-lookup-17bb65be
```

Example prompt: What's the current ETH balance (and its USD value) for the Base mainnet wallet 0x4838B106FCe9647Bdf1E7877BF73cE8B0BAD5f97?

## When to prefer this

Use this endpoint when you specifically need the native ETH balance of a Base mainnet address expressed in both ETH and USD, and don't need token balances, transaction counts, or contract checks. For a fuller wallet overview, prefer the wallet bundle endpoint. For ERC-20 token balances, use the dedicated token balance endpoint.

## Known failure modes

- Missing or malformed address query param — returns error or empty result
- Address not found on Base mainnet (valid format but zero balance — returns 0)
- Invalid 0x address format — returns validation error
- Network/RPC timeout — returns 5xx or gateway error
- Payment not processed (x402 micropayment failure) — returns 402

## How this service works

ETH balance of a Base mainnet address, incl. balance_usd.

## Output

Returns the ETH balance of the specified Base mainnet address as a numeric value, along with its equivalent in USD (balance_usd), enabling quick assessment of a wallet's ETH holdings in both native and fiat terms.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "address": {
       "type": "string",
       "description": "0x-prefixed 20-byte Base address"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "chain": "base",
  "address": "0x4200000000000000000000000000000000000006",
  "balance_eth": 17.2654321,
  "balance_usd": 31886.15,
  "balance_wei": "17265432100000000000"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-mainnet-eth-balance-lookup-17bb65be/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-data-api.sigrunner.workers.dev](https://www.zero.xyz/host/x402-data-api.sigrunner.workers.dev/llms.txt)